Question

When a direct current flows through a straight length of wire, what is the direction of the magnetic field that is produced near the wire?
A) The magnetic field is antiparallel to the direction of the current.
B)The magnetic field is perpendicular to the direction of the current.    
C)The magnetic field is parallel to the direction of the current.
D)There is no magnetic field near a wire carrying direct current; direct currents do not create magnetic fields.

Answer 1

When a current is passing through a conducting wire,there will be the magnetic field is induced around the wire whose fleld(magnetic field) will be directing along the circle around the wire in a plane perpendicular to the line of the wire,with the wire as centre,where the direction of the magnetic field at a point is repesented by the tangent drawn on the circular magnetic field around the wire.

So,Here the megnetic fields will be the concentric circles around the wire prependicular to wire with the wire as center as shown in the figure given.

Also,the direction of the magnetic field around the wire is given by the right hand thumb rule,in which when we grasp the wire with the arm,in such a manner that the thumb indicates the direction of the current,So the fingers indicates the direction of the magnetic field which are always perpendicular to the direction of the current and length of the wire.

So,as per the rule,when the current in the wire is directing upwards the magnetic field around the wire will be anticlockwise and vise versa as shown in the figure.

So,The magnetic field is perpendicular to the direction of the current.(Option B)